Wall thickness and diameter aside, I think 1026 DOM tubing is a wise choice for a roll structure. Although the tensile strength is 25%+/- less than 4130, it has a higher elongation,and is therefore more "tough", or durable. If it bends or deforms in a roll over, well, its done its job.
A cage should be designed for safety first and foremost. Unless you stress relieve a 4130 roll cage, you are undermining the purpose and integrity of the cage. Yes, the 4130 may not deform in a roll over like the DOM (1026, not 1018), but in the example you stated, the rollover in your Silverado at 5,000 lbs. and 80 mph, an improperly fabricated 4130 cage quite possibly would have broken at the weld joints upon impact.
It takes an incredible amount of energy to deform a properly designed structure made from DOM, but only one sharp blow is required to fracture an improperly fabricated 4130 cage. It's the subsequent impacts in a crash that are most dangerous. The impacts that will exploit any part of the stucture that was compromised upon the initial impact.
All that being said, look at an F-1 car. The safety structures are, for the most part, made from carbon filaments or the like, which have literally no elongation compared to metal alloys, and is notch sensitive. Go figure.......In our world, overkill is the key to success, and the impacts that we see are more likely not going to be only frontal or side ones.
